[PATCH v4 1/2] selinux: add brief info to policydb
Stephen Smalley
sds at tycho.nsa.gov
Mon May 15 20:50:22 UTC 2017
On Tue, 2017-05-16 at 03:22 +0900, Sebastien Buisson wrote:
> Add policybrief field to struct policydb. It holds a brief info
> of the policydb, made of colon separated name and value pairs
> that give information about how the policy is applied in the
> security module(s).
> Note that the ordering of the fields in the string may change.
>
> Policy brief is computed every time the policy is loaded, and when
> enforce or checkreqprot are changed.
>
> Add security_policy_brief hook to give access to policy brief to
> the rest of the kernel. Lustre client makes use of this information
> to detect changes to the policy, and forward it to Lustre servers.
> Depending on how the policy is enforced on Lustre client side,
> Lustre servers can refuse connection.
>
> Signed-off-by: Sebastien Buisson <sbuisson at ddn.com>
> ---
> include/linux/lsm_hooks.h | 17 +++++++
> include/linux/security.h | 7 +++
> security/security.c | 8 ++++
> security/selinux/hooks.c | 7 +++
> security/selinux/include/security.h | 2 +
> security/selinux/selinuxfs.c | 2 +
> security/selinux/ss/policydb.c | 88
> +++++++++++++++++++++++++++++++++++++
> security/selinux/ss/policydb.h | 3 ++
> security/selinux/ss/services.c | 68
> ++++++++++++++++++++++++++++
> 9 files changed, 202 insertions(+)
>
> diff --git a/security/selinux/ss/policydb.c
> b/security/selinux/ss/policydb.c
> index 0080122..8ce7f89 100644
> --- a/security/selinux/ss/policydb.c
> +++ b/security/selinux/ss/policydb.c
> @@ -32,13 +32,20 @@
> #include <linux/errno.h>
> #include <linux/audit.h>
> #include <linux/flex_array.h>
> +#include <crypto/hash.h>
> #include "security.h"
>
> #include "policydb.h"
> #include "conditional.h"
> #include "mls.h"
> +#include "objsec.h"
> #include "services.h"
>
> +static unsigned int policybrief_hash_size;
> +static struct crypto_shash *policybrief_tfm;
> +static const char policybrief_hash_alg[] = "sha256";
> +unsigned int policybrief_len;
> +
> #define _DEBUG_HASHES
>
> #ifdef DEBUG_HASHES
> @@ -879,6 +886,8 @@ void policydb_destroy(struct policydb *p)
> ebitmap_destroy(&p->filename_trans_ttypes);
> ebitmap_destroy(&p->policycaps);
> ebitmap_destroy(&p->permissive_map);
> +
> + kfree(p->policybrief);
> }
>
> /*
> @@ -2220,6 +2229,52 @@ static int ocontext_read(struct policydb *p,
> struct policydb_compat_info *info,
> }
>
> /*
> + * Compute summary of a policy database binary representation file,
> + * and store it into a policy database structure.
> + */
> +static int policydb_brief(struct policydb *policydb, void *ptr)
> +{
> + struct policy_file *fp = ptr;
> + u8 *hashval;
> + int rc = 0;
> +
> + if (policydb->policybrief)
> + return -EINVAL;
Should this be a BUG_ON()?
> +
> + hashval = kmalloc(policybrief_hash_size, GFP_KERNEL);
> + if (hashval == NULL)
> + return -ENOMEM;
> +
> + {
> + SHASH_DESC_ON_STACK(desc, policybrief_tfm);
You should be able to move this up to the parent scope now that
policybrief_tfm is allocated at init. No need for a nested block then.
> + desc->tfm = policybrief_tfm;
> + desc->flags = 0;
> + rc = crypto_shash_digest(desc, fp->data, fp->len,
> hashval);
> + if (rc) {
> + printk(KERN_ERR "Failed crypto_shash_digest:
> %d\n", rc);
> + goto out_free;
> + }
> + }
> +
> + /* policy brief is in the form:
> + * selinux(enforce=<0 or 1>:checkreqprot=<0 or
> 1>:<hashalg>=<checksum>)
> + */
> + policydb->policybrief = kasprintf(GFP_KERNEL,
> + "selinux(enforce=%d:checkr
> eqprot=%d:%s=%*phN)",
> + selinux_enforcing,
> + selinux_checkreqprot,
> + policybrief_hash_alg,
> + policybrief_hash_size,
> hashval);
> + if (policydb->policybrief == NULL)
> + rc = -ENOMEM;
> +
> +out_free:
> + kfree(hashval);
> +
> + return rc;
> +}
> +
> +/*
> * Read the configuration data from a policy database binary
> * representation file into a policy database structure.
> */
> @@ -2238,6 +2293,11 @@ int policydb_read(struct policydb *p, void
> *fp)
> if (rc)
> return rc;
>
> + /* Compute summary of policy, and store it in policydb */
> + rc = policydb_brief(p, fp);
> + if (rc)
> + goto bad;
> +
> /* Read the magic number and string length. */
> rc = next_entry(buf, fp, sizeof(u32) * 2);
> if (rc)
> @@ -3456,3 +3516,31 @@ int policydb_write(struct policydb *p, void
> *fp)
>
> return 0;
> }
> +
> +static int __init init_policybrief_hash(void)
> +{
> + struct crypto_shash *tfm;
> +
> + if (!selinux_enabled)
> + return 0;
> +
> + tfm = crypto_alloc_shash(policybrief_hash_alg, 0, 0);
> + if (IS_ERR(tfm)) {
> + printk(KERN_ERR "Failed to alloc crypto hash %s\n",
> + policybrief_hash_alg);
> + return PTR_ERR(tfm);
> + }
> +
> + policybrief_tfm = tfm;
> + policybrief_hash_size =
> crypto_shash_digestsize(policybrief_tfm);
> +
> + /* policy brief is in the form:
> + * selinux(enforce=<0 or 1>:checkreqprot=<0 or
> 1>:<hashalg>=<checksum>)
> + */
> + policybrief_len = 35 + strlen(policybrief_hash_alg) +
> + 2*policybrief_hash_size;
Might as well include the + 1 for the terminating NUL here?
> +
> + return 0;
> +}
> +
> +late_initcall(init_policybrief_hash);
> diff --git a/security/selinux/ss/services.c
> b/security/selinux/ss/services.c
> index 60d9b02..32150fb 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -2170,6 +2170,74 @@ size_t security_policydb_len(void)
> }
>
> /**
> + * security_policydb_brief - Get policydb brief
> + * @brief: pointer to buffer holding brief
> + * @len: in: brief buffer length if no alloc, out: brief string len
> + * @alloc: whether to allocate buffer for brief or not
> + *
> + * On success 0 is returned , or negative value on error.
> + **/
> +int security_policydb_brief(char **brief, size_t *len, bool alloc)
> +{
> + if (!ss_initialized || brief == NULL)
> + return -EINVAL;
> +
> + if (alloc) {
> + /* *brief must be kfreed by caller in this case */
What's the point in putting such a comment here in the code; it is
essentially interface documentation?
> + *brief = kzalloc(policybrief_len + 1, GFP_KERNEL);
> + /*
> + * if !alloc, caller must pass a buffer that
> + * can hold policybrief_len+1 chars
> + */
Ditto. And why not just include the + 1 in the policybrief_len in the
first place?
> + } else if (*len < policybrief_len + 1) {
> + /* put in *len the string size we need to write */
> + *len = policybrief_len;
The caller needs to allocate a buffer of policybrief_len+1, so might as
well include the +1 in the length we return to the caller. Less
opportunity for error.
> + return -ENAMETOOLONG;
> + }
> +
> + if (*brief == NULL)
> + return -ENOMEM;
> +
> + read_lock(&policy_rwlock);
> + *len = policybrief_len;
> + strncpy(*brief, policydb.policybrief, *len);
Why can't we just do a simple strcpy() here?
> + read_unlock(&policy_rwlock);
> +
> + return 0;
> +}
> +
> +void security_policydb_update_info(u32 requested)
> +{
> + /* policy brief is in the form:
> + * selinux(enforce=<0 or 1>:checkreqprot=<0 or
> 1>:<hashalg>=<checksum>)
> + */
> + char enforce[] = "enforce=";
> + char checkreqprot[] = "checkreqprot=";
> + char *p, *str;
> + int val;
> +
> + if (!ss_initialized)
> + return;
> +
> + if (requested == SECURITY__SETENFORCE) {
> + str = enforce;
> + val = selinux_enforcing;
> + } else if (requested == SECURITY__SETCHECKREQPROT) {
> + str = checkreqprot;
> + val = selinux_checkreqprot;
> + }
> +
> + /* update global policydb, needs write lock */
> + write_lock_irq(&policy_rwlock);
> + p = strstr(policydb.policybrief, str);
> + if (p) {
> + p += strlen(str);
> + *p = '0' + val;
> + }
> + write_unlock_irq(&policy_rwlock);
> +}
> +
> +/**
> * security_port_sid - Obtain the SID for a port.
> * @protocol: protocol number
> * @port: port number
--
To unsubscribe from this list: send the line "unsubscribe linux-security-module" in
the body of a message to majordomo at vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
More information about the Linux-security-module-archive
mailing list